This invention relates to a sheeting transport apparatus with which a sheet of material to be scanned, namely, sheeting, is transported with two roller pairs in an auxiliary scanning direction for recording an image on the sheeting or reading the image on the sheeting as it is illuminated with light beams. More particularly, the invention relates to the technical field of sheeting transport apparatus in an optical beam scanner that scans sheeting with light beams deflected or aligned in a one-dimensional direction to record an image on the sheeting (in the case of an image recording apparatus) or read the image recorded on the sheeting (in the case of an image reading apparatus).
In current radiation image information reading apparatus, a stimulable phosphor sheet having radiation energy stored therein as image information is illuminated with exciting light such as laser light so that the stored radiation energy is emitted to produce photo-stimulated luminescence, which is detected with a photodetector such as a photomultiplier to read the radiation image information photoelectrically. For two-dimensional reading of the radiation image information stored in the stimulable phosphor sheet, the optical beam scanner in the radiation image information reading apparatus performs main scanning of the sheet with one-dimensionally deflected laser light as it is transported in an auxiliary scanning direction generally perpendicular to the main scanning direction. A mechanism commonly used in the optical beam scanner to transport the stimulable phosphor sheet or other types of sheeting in an auxiliary scanning direction is a sheeting transport apparatus that employs two roller pairs spaced apart by a distance shorter than the length of the sheeting in the auxiliary scanning direction (see, for example, Unexamined Published Japanese Patent Application (kokai) Nos. 135064/1987, 167150/1987 and 67859/1988).
In the sheeting transport apparatus, the sheeting such as a stimulable phosphor sheet often receives an impact when it goes into or emerges from a pair of rollers. To avoid this problem, one of the two rollers in pair, namely, a nip roller, is brought out of engagement with the other (fixed roller) when the sheeting goes into or emerges from the roller pair. By thusly avoiding the occurrence of impacts on the sheeting, the latter is prevented from vibrating or being offset in position and, as a result, the sheeting is transported in an auxiliary scanning direction smoothly and precisely enough to enable precise reading of the image information. According to commonly assigned Unexamined Published Japanese Patent Application (kokai) No. 281635/1993, there is disclosed an improved mechanism for transporting sheeting in an auxiliary scanning direction using two such roller pairs and it is a compact sheeting transport apparatus of simple construction that uses a single actuator to have the nip roller disengaged from the fixed roller either when the sheeting goes into the roller pair or when it emerges from the roller pair.
In the image recording art, there are used photoprinters with which the images recorded on photographic films such as negatives and reversals (which are hereinafter referred to simply as xe2x80x9cfilmsxe2x80x9d) are printed on light-sensitive materials such as photographic paper and later developed to produce finished photographic prints. Such photoprinters have heretofore been of an analog type that performs areal exposure (direct exposure) of the film image by projecting it onto the light-sensitive material. The assignee has recently commercialized a digital photoprinter which operates in the following manner: the film image is read photoelectrically with an image sensor such as CCD in an image reading apparatus such as a scanner, converted to digital image data which is then subjected to specified image processing schemes in an image processing apparatus; in the optical beam scanner in an image recording apparatus (printing apparatus), a light-sensitive material is scan exposed with recording light beams modulated in accordance with the processed digital image data to record an image (latent image), subjected to development and other necessary treatments with a developing apparatus and output as a finished photographic print.
In the digital photoprinter, the film image is read photoelectrically, converted to digital image information (data) and thereafter subjected to digital image processing in which tonal correction and other schemes are performed to determine the exposing conditions. Therefore, by digital image processing, not only jobs of editing printed images such as assembling a plurality of images and splitting a single image into two or more images but also various image processing schemes such as color/density adjustments, edge enhancement, dodging, peripheral luminance correction, the correction of distortion and the correction of chromatic aberrations can be performed in any desired manner to output prints that meet specific needs of the user. In addition, the image data about the printed images can be supplied to a computer and other processing equipment or stored in recording media such as a floppy disk.
Another advantage of the digital photoprinter is that it is capable of outputting prints of better image quality than those produced by the conventional direct exposure technique in various aspects including resolution, the fidelity in color/density reproduction, and so forth.
Despite these desirable features, the digital photoprinter developed by the assignee has problems. In the image printing apparatus used as an image recorder, a web of light-sensitive material is unreeled and transported in an auxiliary scanning direction as it is repeatedly subjected to main scanning with one-dimensionally deflected light beams so that a number of images are recorded on the uninterrupted length of the light-sensitive material. The exposed light-sensitive material is also developed in a continuous form and finally cut to a specified, image-dependent length, thereby producing discrete finished prints. This approach is capable of volume processing in a very high efficiency. On the other hand, the system is so bulky that small-lot processing can only be accomplished with considerable difficulty. What is more, the system is too expensive and bulky to be suitable for use in small-lot processing.
Under the circumstances, there is a strong need for a printing apparatus that can be used with the digital photoprinter such that a web of light-sensitive material is cut to discrete sheets of a print-dependent length and thereafter scan exposed with light beams. The printing apparatus (which is hereunder referred to as a xe2x80x9csheet-fed image recording apparatusxe2x80x9d) allows for realizing a smaller system and considerable reduction in the equipment and running costs.
One may contemplate operating the sheet-fed image recording apparatus with the sheeting transport apparatus described in Unexamined Published Japanese Patent Application (kokai) No. 281635/1993, supra, that employs two roller pairs and which is used as a mechanism for transporting sheets in an auxiliary scanning direction in an optical beam scanner in a radiation image information reading apparatus.
In the sheet-fed image recording apparatus, a web of light-sensitive material is unreeled and cut to sheets of a given length; therefore, the individual sheets of light-sensitive material are not completely flat but xe2x80x9ccurlxe2x80x9d to some extent. Since the light-sensitive material in a cassette is commonly wound up in roll form with the emulsion-coated side facing outward, a convex curl remains with the emulsion-coated side facing outward after the light-sensitive material has been cut to sheets.
Suppose that such xe2x80x9ccurlingxe2x80x9d sheets of light-sensitive material are transported in an auxiliary scanning direction with the sheeting transport apparatus described in Unexamined Published Japanese Patent Application (kokai) No. 281635/1993, supra that employs two spaced roller pairs. If each sheet of light-sensitive material is exposed imagewise starting at its advancing end, imagewise scan exposure is performed in the image recording (exposing) position between the roller pairs as the sheet is transported in the auxiliary scanning direction in a so-called xe2x80x9ccantileveredxe2x80x9d state (it is nipped by either the upstream or downstream roller pair) in the following two periods, one taken for the advancing end of the sheet to pass through the upstream roller pair and the exposing position to reach the downstream roller pair and the other period taken for the trailing end of the sheet to pass through the upstream roller pair and the exposing position to reach the downstream roller pair. As a consequence, both the advancing and trailing end portions of the curling light-sensitive material experience variations in the optical pathlength in the depth direction, which result in exposure unevenness, hence, density unevenness.
In other words, the sheeting transport apparatus under discussion is capable of reducing to some extent the exposure unevenness (density unevenness) due to load variations such as impact, vibration and positional offset that occur when the sheet of light-sensitive material goes into or emerges from a pair of rollers. However, the apparatus is not primarily intended to prevent the occurrence of curl in the light-sensitive material which is sheeting to be scanned and, hence, it cannot be maintained completely flat in the exposing position. As a result, the problem of exposure unevenness persists.
In short, if two roller pairs used to transport sheets of light-sensitive material are spaced apart by a large distance, more of the light-sensitive material in sheet form is xe2x80x9ccantileveredxe2x80x9d during transport and any curl that is inherent in it becomes correspondingly pronounced in the exposing position, causing scan exposure of the curling and elevated area of the sheet and making impossible to achieve exposure in a uniform and appropriate optical pathlength. As a result, exposure unevenness tends to occur in both the advancing and trailing end portions of the light-sensitive material, making it difficult to obtain prints of high image quality.
The present invention has been accomplished under these circumstances and has as an object providing a small, compact and low-cost sheeting transport apparatus that is simple in configuration and which yet is optimal for precise image reading and recording purposes. The apparatus uses two roller pairs as a component of an auxiliary scan transport mechanism in optical beam scanners and with this apparatus, sheeting or sheets to be scanned such as light-sensitive material in sheet form can be transported smoothly and precisely in an auxiliary scanning direction. In addition, the apparatus is capable of suppressing the adverse effects of curl and other undesirable phenomena in the sheeting; namely, any positional offsets in the depth direction, such as upward departure from the light scanning position that occurs in the advancing and trailing end portions of the sheeting due to curl and other undesirable effects are eliminated or reduced to a very small tolerable limit, thereby ensuring that the sheeting is maintained adequately flat during transport in the auxiliary scanning direction.
This object of the invention can be attained by a sheeting transport apparatus that transports a sheeting on which is performed optical scan in a one-dimensional direction in an auxiliary scanning direction generally perpendicular to the one-dimensional direction, comprising: a first roller pair and a second roller pair that are spaced apart by a distance shorter than a length of the sheeting in the auxiliary scanning direction, wherein the sheeting is transported in the auxiliary scanning direction as it is nipped by the first roller pair and the second roller pair; and an anti-positional offset mechanism that is provided between the first and second roller pairs to ensure that the sheeting has no positional offset from an optical scan position in which the sheeting is scanned optically in a depth direction.
In a preferred embodiment, the anti-positional offset mechanism is provided between the first and second roller pairs at least one of upstream and downstream of the optical scan position of the sheeting. In a further preferred embodiment, the anti-positional offset mechanism is provided between the first and second roller pairs upstream of the optical scan position of the sheeting.
The present invention also provides the sheeting transport apparatus that further comprises: an optical scan guide that is provided between the first and second roller pairs to support the sheeting in the optical scan position from its underside, wherein the anti-positional offset mechanism prevents upward departure of the sheeting from the optical scan guide.
The present invention also provides the sheeting transport apparatus in which the first roller pair is positioned upstream of the second roller pair and includes a first roller driven rotationally and a first nip roller that can move either toward or away from the first roller and the second roller pair is positioned downstream of the first roller pair and includes a second roller driven rotationally and a second nip roller that can move either toward or away from the second roller, and that further comprises: a first opening and closing mechanism that engages the first nip roller and advances or retracts it depending on transport of the sheeting to either open or close the first roller pair; and a second opening and closing mechanism that engages the second nip roller and advances or retracts it depending upon the transport of the sheeting to either open or close the second roller pair.
In each of the embodiment described above, the first opening and closing mechanism is any one of a cam mechanism and a drive unit thereof, a solenoid mechanism, a rotary solenoid mechanism, a rack-and-pinion mechanism and a drive unit thereof as well as a linear guide mechanism and a drive unit thereof, and the second opening and closing mechanism is any one of a cam mechanism and a drive unit thereof, a solenoid mechanism, a rotary solenoid mechanism, a rack-and-pinion mechanism and a drive unit thereof as well as a linear guide mechanism and a drive unit thereof.
In another preferred embodiment, the first opening and closing mechanism comprises a first cam mechanism and a drive unit of the first cam mechanism, and wherein the second opening and closing mechanism comprises a second cam mechanism and a drive unit of the second cam mechanism.
In still another preferred embodiment, the drive unit of the first cam mechanism and the drive unit of the second cam mechanism are a single common drive source that drives the first and second cam mechanisms in unison such that the first roller pair or the second roller pair is selectively opened and closed.
In yet another preferred embodiment, the first cam mechanism has: a first rocking member that rotatably supports the first nip roller; and a first cam member that engages the first rocking member to move the first nip roller either toward or away from the first roller; the second cam mechanism has: a second rocking member that rotatably supports the second nip roller; and a second cam member that engages the second rocking member to move the second nip roller either toward or away from the second roller; and the first and second cam members have: a single common rotating shaft to which the single common drive source working as a rotational drive source is coupled.
In another preferred embodiment, the first rocking member has: a first bracket that rotatably supports the first nip roller and makes reciprocal movements to come closer to or depart from the first roller; a first pivoting member that pivots in engagement with the first bracket member and the first cam member; and a first urging device that urges the first bracket such that the first nip roller is pressed against the first roller; and the second rocking member has: a second bracket that rotatably supports the second nip roller and makes reciprocal movements to come closer to or depart from the second roller; a second pivoting member that pivots in engagement with the second bracket and the second cam member; and a second urging device that urges the second bracket such that the second nip roller is pressed against the second roller.
In still another preferred embodiment, the first and second cam members are a single common eccentric cam and the first and second pivoting members have a single common pivoting shaft.
In yet another preferred embodiment, the anti-positional offset mechanism comprises: a retaining roller pair for nipping the sheeting to be held in the optical scan position and a nipping force adjusting mechanism, the retaining roller pair having a rotatable fixed roller and a rotatable retainer roller which is adjustable in a nipping force that nips the sheeting in cooperation with the fixed roller, and the nipping force adjusting mechanism engaging the retainer roller to adjust the nipping force by which the sheeting is nipped between the retainer roller and the fixed roller.
In another preferred embodiment, the nipping force adjusting mechanism comprises a third rocking member that rotatably supports the retainer roller, a third urging device that urges the rocking member such that the retainer roller is pressed against the fixed roller, and an urging force adding device that adds or relieves an urging force by which the third urging device urges the third rocking member.
In still another preferred embodiment, the urging force adding device adds or relieves the urging force by which the third urging device urges the third rocking member depending upon whether the first nip roller is moved toward or away from the first roller by means of the first cam mechanism.
In yet another preferred embodiment, the urging force adding device relies upon the first rocking member in the first cam mechanism to add or relieve the urging force by which the third urging device urges the third rocking member.
In another preferred embodiment, the urging force adding device further includes a fourth rocking member that engages the first bracket in the first rocking member in the first cam mechanism, the third rocking member has a rocking shaft through the fourth rocking member, the third urging device urges the third rocking member with respect to the fourth rocking member, and the reciprocal movements of the first bracket help add and relieve the urging force by which the third urging device urges the third rocking member.
In still another preferred embodiment, the third rocking member is split into more than one segment in the main scanning direction and each segment has the retainer roller, the fixed roller and the third urging device.
In yet another preferred embodiment, the retainer roller for each segment is subdivided into smaller sub-segment rollers, the fixed roller for each segment is subdivided into two subdivided rollers that are provided only at both ends of the third rocking member and that are respectively in contact with the smaller sub-segment rollers of the retainer roller at both ends.
In another preferred embodiment, each of the retainer roller and the fixed roller has split rollers.
In still another preferred embodiment, the fixed roller is rotatably supported on the optical scan guide.
In yet another preferred embodiment, the sheeting transport apparatus is an auxiliary scan transport mechanism of an image recording apparatus and the sheeting is a light-sensitive material, and wherein the fixed roller is provided so as to avoid a back print position or back print positions used for back printing with a back printer, when the image recording apparatus comprises the back printer.
In another preferred embodiment, the optical scan guide has a plurality of curved pawls in a comb shape which are provided in the one-dimensional direction, which extend upstream in the auxiliary scanning direction and each of which has a forward end being curved inwardly.
In still another preferred embodiment, the optical scan guide has a plurality of straight pawls in a comb shape which are provided in the one-dimensional direction and which extend downstream in the auxiliary scanning direction.